As I study this video more and more (yep, we just keep looking at things because we are that nerdy and that paranoid that we missed something) I saw at least 3 very subtle findings.

Watch the video of this right handed physical therapist who had L knee reconstruction (MCL/ACL with hamstring allograft) a few (hundred) times and see what you come up with, then come back and read this. We lie to slow things down and even frame by frame it with the slow motion feature or space bar to stop it. As background to the clinical exam, he has limited hip and knee extension on the left, 4/5 weakness of the quadratus femoris. His popliteus tests strong and 5/5. He has right sided back pain with L sided knee pain at the joint line and just inferior and medial. the treadmill is at a 2% grade at 2 mph.

Notice how he has a pelvic drift to the right during stance phase on that side. Why do you think? Remember, he has had a left sided knee surgery that left him with limited knee extension on that side. This creates a functional short leg on that side (the left), so he needs to get the longer (right) leg around. We don’t always see lateral movement of the pelvis on the longer leg side, but our guess is he is trying to “shorten” the longer leg side; lateral translation in the coronal plane is one strategy to accomplish that.

Now look at the left side. Can you see the subtle hip hike to clear the right leg? How about the small amount of circumduction? Sometimes folks will employ more than one strategy to get around a long leg, but ususally one will predominate, but not in this case.

Did you catch the abductory twist of the right heel? The longer leg side needs to go through a greater range of motion of ankle dorsiflexion which will store more potential energy in the tricep surae as well as long flexors of the toes, that energy needs to go somewhere!

Now think about step length. It will often be shortened on the shorter leg side. He still needs to move forward the same amount, so he uses the right arm to help propel his center of mass forward. Do you see the increased arm swing?

And why does he abduct his right arm so much? Where is his center of mass at left foot strike? It is all the way to the right, because of the “short leg”, correct? How can you counterbalance that? Abducting the arm would certainly accomplish that. Why does it go across the body? It is no longer needed to be that lateral during stance phase on the right, but he still needs to use it to propel himself forward with the shortened step length we talked about before.

Mental gymnastics, running through what runs through our minds and why things may appear the way that they do. A great lesson in knowing what is supposed to happen and when in the gait cycle